DRAFT Inventory of U.S Greenhouse Gas Emissions and Sinks

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 2016) based on reported facility level data for years 2010 through 2015. The amount of CO 2 captured/recovered for on-site process use is deducted from the total potential emissions (i.e., from lime production and LKD). The net lime emissions are presented in Table 4-6 and Table 4-7. GHGRP data on CO 2 removals (i.e., CO 2 captured/recovered) was available only for 2010 through 2015. Since EPA’s GHGRP data are not available for 1990 through 2009, IPCC “splicing” techniques were used as per the 2006 IPCC Guidelines on time series consistency (IPCC 2006, Volume 1, Chapter 5). Lime production data (by type, high-calcium- and dolomitic-quicklime, high-calcium- and dolomitic-hydrated, and dead-burned dolomite) for 1990 through 2015 (see Table 4-8) were obtained from the U.S. Geological Survey (USGS) (USGS 2016b; Corathers 2017) annual reports and are compiled by USGS to the nearest ton. Natural hydraulic lime, which is produced from CaO and hydraulic calcium silicates, is not manufactured in the United States (USGS 2011). Total lime production was adjusted to account for the water content of hydrated lime by converting hydrate to oxide equivalent based on recommendations from the IPCC, and is presented in Table 4-9 (IPCC 2006). The CaO and CaO•MgO contents of lime were obtained from the IPCC (IPCC 2006). Since data for the individual lime types (high calcium and dolomitic) were not provided prior to 1997, total lime production for 1990 through 1996 was calculated according to the three year distribution from 1997 to 1999. Table 4-8: High-Calcium- and Dolomitic-Quicklime, High-Calcium- and Dolomitic-Hydrated, and Dead-Burned-Dolomite Lime Production (kt) High-Calcium Dolomitic High-Calcium Dolomitic Dead-Burned Year Quicklime Quicklime Hydrated Hydrated Dolomite 1990 11,166 2,234 1,781 319 342 2005 14,100 2,990 2,220 474 200 2011 13,900 2,690 2,010 230 200 2012 13,600 2,790 2,000 253 200 2013 13,800 2,850 2,050 260 200 2014 14,100 2,740 2,190 279 200 2015 13,100 2,550 2,150 279 200 18 Table 4-9: Adjusted Lime Production (kt) Year High-Calcium Dolomitic 1990 12,466 2,800 2005 15,721 3,522 2011 15,367 3,051 2012 15,075 3,076 2013 15,297 3,252 2014 15,699 3,135 2015 14,670 2,945 Note: Minus water content of hydrated lime. 19 20 21 22 23 Uncertainty and Time-Series Consistency – TO BE UPDATED FOR FINAL INVENTORY REPORT The uncertainties contained in these estimates can be attributed to slight differences in the chemical composition of lime products and CO 2 recovery rates for on-site process use over the time series. Although the methodology accounts for various formulations of lime, it does not account for the trace impurities found in lime, such as iron 4-12 DRAFTInventoryof U.S. GreenhouseGasEmissionsandSinks: 1990–2015

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 oxide, alumina, and silica. Due to differences in the limestone used as a raw material, a rigid specification of lime material is impossible. As a result, few plants produce lime with exactly the same properties. In addition, a portion of the CO 2 emitted during lime production will actually be reabsorbed when the lime is consumed, especially at captive lime production facilities. As noted above, lime has many different chemical, industrial, environmental, and construction applications. In many processes, CO 2 reacts with the lime to create calcium carbonate (e.g., water softening). Carbon dioxide reabsorption rates vary, however, depending on the application. For example, 100 percent of the lime used to produce precipitated calcium carbonate reacts with CO 2; whereas most of the lime used in steel making reacts with impurities such as silica, sulfur, and aluminum compounds. Quantifying the amount of CO 2 that is reabsorbed would require a detailed accounting of lime use in the United States and additional information about the associated processes where both the lime and byproduct CO 2 are “reused” are required to quantify the amount of CO 2 that is reabsorbed. Research conducted thus far has not yielded the necessary information to quantify CO 2 reabsorption rates. 9 However, some additional information on the amount of CO 2 consumed on site at lime facilities has been obtained from EPA’s GHGRP. In some cases, lime is generated from calcium carbonate byproducts at pulp mills and water treatment plants. 10 The lime generated by these processes is included in the USGS data for commercial lime consumption. In the pulping industry, mostly using the Kraft (sulfate) pulping process, lime is consumed in order to causticize a process liquor (green liquor) composed of sodium carbonate and sodium sulfide. The green liquor results from the dilution of the smelt created by combustion of the black liquor where biogenic carbon (C) is present from the wood. Kraft mills recover the calcium carbonate “mud” after the causticizing operation and calcine it back into lime—thereby generating CO 2—for reuse in the pulping process. Although this re-generation of lime could be considered a lime manufacturing process, the CO 2 emitted during this process is mostly biogenic in origin, and therefore is not included in the industrial processes totals (Miner and Upton 2002). In accordance with IPCC methodological guidelines, any such emissions are calculated by accounting for net C fluxes from changes in biogenic C reservoirs in wooded or crop lands (see the Land Use, Land-Use Change, and Forestry chapter). In the case of water treatment plants, lime is used in the softening process. Some large water treatment plants may recover their waste calcium carbonate and calcine it into quicklime for reuse in the softening process. Further research is necessary to determine the degree to which lime recycling is practiced by water treatment plants in the United States. Another uncertainty is the assumption that calcination emissions for LKD are around 2 percent. The National Lime Association (NLA) has commented that the estimates of emissions from LKD in the United States could be closer to 6 percent. They also note that additional emissions (approximately 2 percent) may also be generated through production of other byproducts/wastes (off-spec lime that is not recycled, scrubber sludge) at lime plants (Seeger 2013). There is limited data publicly available on LKD generation rates and also quantities, types of other byproducts/wastes produced at lime facilities. Further research and data is needed to improve understanding of additional calcination emissions to consider revising the current assumptions that are based on IPCC guidelines. In preparing estimates for the current inventory, EPA initiated a dialogue with NLA to discuss data needs to generate a country specific LKD factor and is reviewing the information provided by NLA. More information can be found in the Planned Improvements section below. The results of the Approach 2 quantitative uncertainty analysis are summarized in Table 4-10. Lime CO 2 emissions for 2015 were estimated to be between 13.8 and 14.5 MMT CO 2 Eq. at the 95 percent confidence level. This confidence level indicates a range of approximately 3 percent below and 3 percent above the emission estimate of 14.1 MMT CO 2 Eq. 9 Representatives of the National Lime Association estimate that CO2 reabsorption that occurs from the use of lime may offset as much as a quarter of the CO2 emissions from calcination (Males 2003). 10 Some carbide producers may also regenerate lime from their calcium hydroxide byproducts, which does not result in emissions of CO2. In making calcium carbide, quicklime is mixed with coke and heated in electric furnaces. The regeneration of lime in this process is done using a waste calcium hydroxide (hydrated lime) [CaC2 + 2H2O C2H2 + Ca(OH) 2], not calcium carbonate [CaCO3]. Thus, the calcium hydroxide is heated in the kiln to simply expel the water [Ca(OH)2 + heat CaO + H2O] and no CO2 is released. Industrial Processes and Product Use 4-13